errors: move similarity_hint() to error module

errors: move similarity_hint() to error module

I want to be able to reuse it from `UnknownIdentifier`'s constructor.

Moving it results in a new import of `difflib` in the `error`
module. There was a comment at the top of `error.py` saying "Do not
import anything but pycompat here, please", which was added (except
for the "pycompat" bit) in 08cabecfa8a8 (errors: move revlog errors,
2009-01-11). I don't know the reason for the comment. I'm guessing the
point was to not make the module depend on other Mercurial modules. If
that was it, then importing `difflib` should be fine.

Sorry about the churn (I moved this code from the `dispatch` module to
the `scmutil` module very recently).

Differential Revision: https://phab.mercurial-scm.org/D9345

--- a/mercurial/dispatch.py	Thu Nov 19 09:19:44 2020 -0800
+++ b/mercurial/dispatch.py	Thu Nov 19 12:20:26 2020 -0800
@@ -484,10 +484,10 @@
         except (error.UnknownCommand, error.Abort):
             suggested = False
             if inst.all_commands:
-                sim = scmutil.getsimilar(inst.all_commands, inst.command)
+                sim = error.getsimilar(inst.all_commands, inst.command)
                 if sim:
                     ui.warn(nocmdmsg)
-                    ui.warn(b"(%s)\n" % scmutil.similarity_hint(sim))
+                    ui.warn(b"(%s)\n" % error.similarity_hint(sim))
                     suggested = True
             if not suggested:
                 ui.warn(nocmdmsg)

--- a/mercurial/error.py	Thu Nov 19 09:19:44 2020 -0800
+++ b/mercurial/error.py	Thu Nov 19 12:20:26 2020 -0800
@@ -13,6 +13,8 @@
 
 from __future__ import absolute_import
 
+import difflib
+
 # Do not import anything but pycompat here, please
 from . import pycompat
 
@@ -270,6 +272,25 @@
     __bytes__ = _tobytes
 
 
+def getsimilar(symbols, value):
+    sim = lambda x: difflib.SequenceMatcher(None, value, x).ratio()
+    # The cutoff for similarity here is pretty arbitrary. It should
+    # probably be investigated and tweaked.
+    return [s for s in symbols if sim(s) > 0.6]
+
+
+def similarity_hint(similar):
+    from .i18n import _
+
+    if len(similar) == 1:
+        return _(b"did you mean %s?") % similar[0]
+    elif similar:
+        ss = b", ".join(sorted(similar))
+        return _(b"did you mean one of %s?") % ss
+    else:
+        return None
+
+
 class UnknownIdentifier(ParseError):
     """Exception raised when a {rev,file}set references an unknown identifier"""
 

--- a/mercurial/scmutil.py	Thu Nov 19 09:19:44 2020 -0800
+++ b/mercurial/scmutil.py	Thu Nov 19 12:20:26 2020 -0800
@@ -7,7 +7,6 @@
 
 from __future__ import absolute_import
 
-import difflib
 import errno
 import glob
 import os
@@ -143,23 +142,6 @@
         ui.status(_(b"no changes found\n"))
 
 
-def getsimilar(symbols, value):
-    sim = lambda x: difflib.SequenceMatcher(None, value, x).ratio()
-    # The cutoff for similarity here is pretty arbitrary. It should
-    # probably be investigated and tweaked.
-    return [s for s in symbols if sim(s) > 0.6]
-
-
-def similarity_hint(similar):
-    if len(similar) == 1:
-        return _(b"did you mean %s?") % similar[0]
-    elif similar:
-        ss = b", ".join(sorted(similar))
-        return _(b"did you mean one of %s?") % ss
-    else:
-        return None
-
-
 def formatparse(write, inst):
     if inst.location is not None:
         write(
@@ -170,8 +152,8 @@
         write(_(b"hg: parse error: %s\n") % inst.message)
     if isinstance(inst, error.UnknownIdentifier):
         # make sure to check fileset first, as revset can invoke fileset
-        similar = getsimilar(inst.symbols, inst.function)
-        hint = similarity_hint(similar)
+        similar = error.getsimilar(inst.symbols, inst.function)
+        hint = error.similarity_hint(similar)
         if hint:
             write(b"(%s)\n" % hint)
     elif inst.hint: